Auxiliary circuit



Feb. 23, 1937. H. E. YOUNG 2,071,911

' AUXILIARY CIRCUIT Filed March 24, 1934 Patented Feb. 23, 1937 UNITED STATES} PATENT OFFICE AUXILIARY CIRCUIT Hugh E. Young, Chicago, Ill.

Application March 24, 1934, Serial No. 717,280 (01. 171-91) 3 Claims.

The present invention relates to illuminated safety signs and the like. A suitable example is a boulevard stop sign. The effectiveness of such a safety sign depends upon maintaining the 5 illumination. If an electric light be employed for such illumination, the burning out of the lght killsthe value of the sign. My invention aims to provide a simple means for bringing into action automatically and without any moving parts a secondary lamp in case the primary lamp burns out. I

The prime requisite in such a sign is reliability,

i. e., continuity of performance. The ability to preserve the spare lamp without deterioration is while making it instantly and unfailingly available upon burning out of the primary lamp is an important aspect of my invention.

One feature of this invention is that failure of the primary lamp immediately causes illumination of an auxiliary lamp; another feature of this invention is that it employs no mechanical relays or moving parts of any kind; still another feature of this invention is that the auxiliary lamp has substantially no current flow therethrough while the primary lamp is functioning;

still other features and advantages of this. invention will appear from the following specification and drawing, in which- The single figure is a diagrammatic view, illustrating the relation of the primary and auxiliary lamps.

i In some particular fields of illumination, as for example through-street stop signs or theatre exit lights, it is desirable to have a second or auxiliary lamp which will automatically function upon the failure of the primary lamp to illuminate the sign, yet'draw no current while said primary lamp is functioning properly. This has been achieved by the use of relays of vari- 40 ous forms, but much trouble has been experienced due to corrosion and sticking of the contact points, and to other mechanical defects in the relays. This invention overcomes these previous defects by providing an electrical circuit which is in perfect balance while the primary lamp functions properly, but when unbalanced ,by failure of the primary lamp causes the illumination of the sign by an auxiliary lamp.

In the embodiment of this invention illustrated in the drawing, a primary lamp III is balanced by a variable resistance II, which variable resistance is adjusted to match the impedance of the filament of the primary lamp. In series with the primary lamp and connected thereto by a lead I4 is a fixed resistance l2, while the variable resistance II has in series with it a second fix'ed resistance I 3 connected thereto by a lead I5. These two series branches are connected in parallel to a sourceof electrical energy by the leads I6 and II. An auxiliary lamp I8 is placed across the two branches by connecting it to the leads II and I5.

In the particular embodiment of this invention designed to be used in illuminating a through street stop sign, and to be operable from the common commercial source of current at about volts, the resistances l2 and I3 are of 1,000 ohms each; the filament resistance of the primary lamp I0 is of about the same value; the variable resistance II has a range permitting it to be matched to the filament impedance of the primary lamp; and theauxiliary lamp I8 has a relatively low filament resistance, in the neighborhood of 50 ohms.

So long as the lamp I0 is not burned out, it

, will continue to illuminate the sign by current flow from the wire I! through the lamp Ill, wire I4, resistance I2 and wire I6. Current will also fiow through the resistances II and I3 in series, these resistances being bridged across the supply circuit I6 and II. The lamp I8 is connected at equi-potential points, that is, at the midpoint between resistance I2 and lamp II) at one end, and between resistance I3 and resistance II at the other end, whereby the lamp I8 normally has no current or substantially-no current fiow through it, and it will remain indefinitely available for service. I

In the event that the lamp [0 burns out, the circuit becomes unbalanced and current will fiow through the resistance I I, lamp I8 and resistance I2 in one branch, and through the resistance I3 alone in another branch to the return conductor I6. It will be observed that no movable parts, switching contacts or the like are required, and that this circuit will bring the lamp I8 into play with the utmost reliability when the lamp l0 burns out. The operation of the device is entirely independent of voltage and over voltage is not able to damage the lamp I8, since both terminals of the lamp are at the same potential so long as the lamp III is unimpaired.

The bridge circuit utilized in this invention does not necessarily consist of resistance alone, but may have all or some of its legs composed of inductance or capacitance, or any combination of resistance, inductance and capacitance resulting in balanced impedances with the particular form of current being used.

What I regard as new, and desire to secure by Letters Patent, is:

first of which consists of a primary lamp and an impedance, said lamp being adapted to supply the desired illumination for the stop sign, and the second branch of which consists of a second impedance and a third impedance; and an aux iliary lamp in a circuit from the connection between the primary lamp and impedance in the first branch to the connection between the second and third impedances in the second branch, said auxiliary lamp having a much lower filament impedance than said primary lamp and being adapted to illuminate said stop sign upon failure of said primary lamp.

2. A stop sign lighting circuit of the character described, including: a primary lamp and fixed impedance connected in series, said lamp having a filament impedance of substantially one thousand ohms and being adapted to supply the desired illumination for the stop sign with which the circuit is used; a variable impedance and a second fixed impedance connected in a second series, said second series being connected in parallel with said first series; a source of commercial A. C. power whereby said two parallel series are energized; and an auxiliary lamp connected from the juncture of said primary lamp and said fixed impedance to the juncture of said variable impedance and said second fixed impedance, said auxiliary lamp having a filament impedance substantially lower than that of said primary lamp and being adapted to furnish illumination for said stop sign upon the failure of said primary lamp.

3. The combination for illuminating a safety sign, comprising a current supply circuit, a primary lamp normally adapted to illuminate the sign by current flow therethrough, an impedance in series therewith, said lamp and impedance being connected in series and bridged across the supply circuit, a shunt circuit comprising two impedances connected in series and being bridged across the supply circuit, a stand-by lamp also adapted when energized to illuminate said sign, said stand-by lamp being connected to the two bridge circuits at equi-potential points ,whereby the stand-by lamp is substantially free of vcurrent flow so long as the primary lamp is intact, said stand-by lamp being supplied with current flow by shift of potential of the points to which the spare lamp is connected by interruption of the circuit through the primary lamp.

HUGH E. YOUNG. 

